> Why is protanopia like deuteranopia? Red and green colorblind deficiencies (deuteranopia and protanopia) are very similar, as these cones often overlap. Therefore, protanopia and deuteranopia can often eliminate the ability to see both red and green, showing the world in vibrant blues and yellows, as well as very similar browns, oranges, reds, and greens.
> People with deuteranomaly and protanomaly are often incorrectly diagnosed collectively as ‘red-green’ colour blind because both types generally have difficulty distinguishing between reds, greens, browns and oranges. They also commonly confuse different types of blue and purple hues and many other colour combinations.
> The answer is that dichromatic colorblindness is imitated by assuming two of the three types of receptors receive the same light input. In deuteranopia, for example, the assumption is that the neural receptors expecting medium (M) and long (L) wavelength light are both receiving signals from cones with long (L) pigments. This results in the yellow you noticed. Note also that deuteranopia and protanopia don’t result in exactly the same hue of yellow because of the difference between their peak sensitivities. In one case it is assumed all signals are coming from L pigments and in the other all from M pigments.